Communication networks typically include transmission of modulated signals. The transmission of the signals is generally regulated by a standard. One characteristic of the transmission that is typically regulated is the transmission frequency (band). Some standards include multiple bands (or channels), and therefore, require transceivers that are operable over the multiple transmission bands. Generally, the transceivers frequency up-convert signals before transmission, and frequency down-convert signals after reception. The frequency conversions typically require local oscillators, and transceivers that support multiple bands require local oscillators that operate at multiple frequencies.
Examples of wireless communication systems that employ frequency hopping transceivers include unlicensed cordless phones operating according to the FCC part 15 requirements as well as OFDM (orthogonal frequency duplex multiplexing) UWB (ultra wideband) radios as defined according to the WiMedia UWB standard. Frequency hopping transceivers frequency hop between multiple transmission bands and, therefore, typically require local oscillators that can switch frequencies.
FIG. 1 shows an example of an indoor broad band wireless communication network 100 such as a UWB network. As mentioned, embodiments of WiMedia UWB networks include frequency hopping. The exemplary network 100 includes a high definition television (HDTV) monitor 110 networked with other devices, such as, a digital video recorder (DVR) 120, a digital video disk (DVD) player 140 and a computing device 130.
A prior method of providing switching frequencies includes switching the divide ratio in a phase lock loop (PLL). However, this method generally provides very slow switching times (on the order of micro- or milli-seconds). Another method includes running multiple PLLs in parallel and switching between the PLL outputs with an analog signal multiplexer. However, this method consumes significant amounts of power and results in significant leakthrough from the un-selected PLLs. Another method includes generating the LO frequency by dividing down a single high-frequency sinusoid and then re-combining the various sub-harmonics using mixers and analog signal multiplexers to create the hopping LO signal. However, this method consumes a lot of power and results in a significant number of spurious outputs. For integrated circuits, this method requires many inductors which take up significant amounts of die space.
It is desirable to provide methods and apparatuses for generation of fast frequency switching local oscillator signals. It is desirable that the methods and apparatuses be low-cost, low-power and can be implemented using minimal amounts of circuitry.